The intravenous infusion of fluids into a patient's bloodstream is a common medical procedure. Fluids that are typically administered intravenously include glucose and saline solutions, drugs, and blood. Intravenous (IV) systems generally comprise a reservoir, a dripper, a feed tube, and an IV needle. The reservoir, also called an IV bag, holds a quantity of the fluid to be infused. The reservoir is coupled to a dripper by means of a feed tube. The dripper, in turn, is coupled by the feed tube to the hollow IV needle, which is injected into a vein of the patient. The fluid in the reservoir drips by gravity flow through the needle and into the bloodstream, with the drip rate being controlled by the dripper.
It is imperative that an IV system be carefully monitored for a number of reasons. First, since the fluids that are administered are often life-maintaining solutions, such as drug solutions, the reservoir must never be allowed to empty for prolonged periods. Harmful or even fatal consequences may otherwise result. In addition, if the IV system runs out of fluid, blood will flow back from the patient and clot inside the needle. If this happens, the needle must be replaced by a new needle, with the replacement procedure being painful for the patient and time-consuming for the hospital staff. Hence, the IV system requires frequent inspection by the hospital staff. However, the shortages of qualified staff and high costs characterizing hospitals today make it difficult to administer such thorough patient care.
As a result, several types of devices to automatically monitor the amount of fluid remaining in an IV system have been developed. One group of devices makes use of a scale mechanism, such as a seesaw. When the amount of remaining fluid falls below some predetermined value, the seesaw tilts and actuates an electrical switch to trigger an alarm. Although these scale-based devices are simple, the springs used in the scales are quite sensitive to jolts or shocks that can occur, for example, if the patient accidentally strikes the device.
Another type of prior art device makes use of a clip or clamp together with elements that complete an electrical signalling circuit as the reservoir bag collapses on emptying. The chief disadvantage of such clamp-based devices are that the clamp can affect the rate of flow of the IV fluid and that the alerting signal is only activated when the reservoir is empty, as opposed to it being nearly empty.
Still another prior art device uses optical sensing equipment to sense the fluid level of the dripper and to monitor the IV for occlusion or bubbles in the fluid. Here, the disadvantage lies in the complexity and high cost of such equipment.